Purkinje Effect - Use of Red Lights

Use of Red Lights

The insensitivity of rods to long-wavelength light is related to the use of red lights under certain special circumstances – for example, in the control rooms of submarines, in research laboratories, aircraft, or during naked-eye astronomy.

Under conditions where it is desirable to have both the photopic and scotopic systems active, red lights provide a solution. Submarines are dimly lit to preserve the night vision of the crew members working there, but the control room must be lit to allow crew members to read instrument panels. By using red lights, or wearing red goggles, the cones can receive enough light to provide photopic vision (namely the high-acuity vision required for reading). The rods are not saturated by the bright red light because they are not sensitive to long-wavelength light, however, so the crew members remain dark adapted, in case they need to look through the periscope at night, for example. Similarly, airplane cockpits use red lights so pilots can read their instruments and maps while maintaining night vision to see outside of the aircraft.

Red lights are also often used in research settings. Many research animals (such as rats and mice) have limited photopic vision - as they have far fewer cone photoreceptors. By using red lights, the animal subjects remain "in the dark" (the active period for nocturnal animals), but the human researchers, who have one kind of cone that is sensitive to long wavelengths, are able to read instruments or perform procedures that would be impractical even with fully dark adapted (but low acuity) scotopic vision. For the same reason, zoo displays of nocturnal animals often are illuminated with red light.